% The New Year's Party Problem

% PROGRAM 6 in 
%    http://www.cs.utexas.edu/users/vl/tag/seating_solutions 

:- sorts table; chair; guest.

:- variables
	G,G1 :: guest;
	T :: table;
	C :: chair.

:- constants
	1..N :: table;
	1..M :: chair;
	1..N*M :: guest;
	likes(guest,guest), 
	dislikes(guest,guest),
	assign_table(guest,table),
	assign_chair(guest,chair) :: cwAtomicFormula.

% start with an arbitrary arrangement.
assign_table(G,T) :- not (not assign_table(G,T)).
assign_chair(G,C) :- not (not assign_chair(G,C)).

% make sure that everyone sits at a chair at some table,
:- not \/T: assign_table(G,T).
:- not \/C: assign_chair(G,C).

% that no two guests sit at the same chair,
:- assign_table(G,T), assign_table(G1,T),
   assign_chair(G,C), assign_chair(G1,C), G < G1.

% that the ones who like each other sit at the same table,
:- not assign_table(G,T), likes(G,G1), assign_table(G1,T).

% and that the ones who do not like each other do not sit at 
% the same table.
:- assign_table(G,T), dislikes(G,G1), assign_table(G1,T).

% display the arrangement only.
:- show assign_table(G,T).